The present invention is generally in the area of cell culture and transplantation and specifically is directed to methods and compositions for enhancing cell survival.
The United States government has rights in this invention by virtue of a grant from the National Science Foundation BCS9202311 to Robert S. Langer.
Liver transplantation is the established therapy for end-stage liver disease, as described by Starzl, et al. N. Eng. J. Med. 321:1014-1022 (1989), but this therapy is greatly limited by a scarcity in donor organs. Approximately 30,000 people still die each year in the United States of liver disease (American Liver Foundation, Vital Statistics of the United States, 1988; Vol. 2(A)), and 23% of those listed for transplantation in 1991 died while waiting for an organ (Annual report of the U.S. scientific registry for organ transplantation and the organ procurement and transplant network, 1990. Richmond, Va., UNOS, and Bethesda, Md., the Division of organ transplantation, Health Resources and Services Administration, PE59, 19). Transplantation of parenchymal liver cells, hepatocytes, has been proposed as an alternative to whole organ transplantation for liver disease (Asonuma, et al. J. Ped. Surg., 27:298-301 (1992)). Single metabolic deficiencies may be cured with replacement of 12% of liver mass (Asonuma, et al.), and thus a single liver could be utilized for several patients, or partial resection of a living donor's liver could provide the necessary liver mass to treat another person. Alternatively, a patient's own cells could be harvested, genetically modified, and delivered back to the person to treat single gene defects (Wilson, et al., J. M., Grossman, M., Raper, S. E., Baker, J. R., Newton, R. S., Thoene, J. G. Ex vivo gene therapy of familial hypercholesteremia. Human Gene Therapy, 1992; 3:179-222). Hepatocytes have been previously transplanted in suspension, encapsulated, adherent to microspheres, or adherent to degradable or non-biodegradable polymer fibers (Hansen, et al., Hepatocytes transplantation using artificial biodegradable polymers. In: Hoffman, M. A., Ed. Current controversies in biliary atresia. Austin, Tex.: R. G. Landes, 1993; 96-106).
To replace liver function utilizing hepatocyte transplantation, regardless of the means of cell delivery, it will be critical to ensure the survival and growth of the transplanted cells. Previous studies on hepatocyte transplantation have indicated that performing a portal caval shunt (PCS) in conjunction with hepatocyte transplantation improves hepatocyte engraftment (Uyama, et al., Transplantation 55:932-935 (1993)). However, patients in liver failure are already in a compromised situation, and the burden of a PCS may not be feasible for this population.
The liver is capable of repeatedly regenerating after partial hepatectomy, and a variety of factors have been identified that induce hepatocyte growth. These include epidermal growth factor (EGF), alpha fibroblastic growth factor, hepatocyte growth factor, and transforming growth factor alpha (Fausto Prog. Growth Factor Res., 3:219-234 (1991)). The effects of these mitogens can be mediated with comitogens such as insulin, glucagon, and estrogen. Many of the factors important in hepatic regeneration appear to be present in the portal circulation (Jaffe, et al., Int. J. Exp. Path., 72:289-299 (1991)), and although the origin of the factors is not clear, trophic factors from islet cells improve the survival of transplanted hepatocytes (Ricordi, et al., Surgery, 105:218-223 (1989)). However, it is difficult to attribute these effects to the presence of specific factors, and these approaches are limited by the shortage of available islet tissue. If techniques to reproducibly deliver given amounts of specific factors were developed it would allow one to systematically investigate the effects of various factors, alone and in combination, on hepatocyte survival and growth, and it could potentially move hepatocyte transplantation closer to a clinically relevant therapy.
Systems to deliver macromolecules, such as proteins, over sustained periods have been in active development over the past 20 years, as reviewed by Langer, Science, 249:1527-1533 (1990). Delivery vehicles fabricated from biodegradable polymers are especially attractive, as the drug delivery can be controlled by diffusion through the polymer backbone and/or by erosion of the polymer. Systems to deliver factors relevant to hepatocytes, such as insulin (Brown, et al., Diabetes, 35:684-691 (1986)) and EGF (Murray, et al., In Vitro, 1983; 10:743-748) have been previously developed. However, small quantities of biologically active factors could be released over extended periods with these systems, but the form of the devices (solid polymer slabs) was not suitable for co-transplantation with cells.
It would therefore be advantageous to have a system for delivery of factors enhancing cell survival, proliferation, and maintaining the cells in a differentiated form which is reproducible, easily manufactured, in a form suitable for implantation with cells, and highly controllable.